Cycle and ovulation

Timing tools for anyone tracking a cycle or trying to conceive. Free, and none of them are contraception.

Example answerDay 14 likely ovulationFertile days 9 to 15, in a 28-day cycleWhen am I most fertile?You need: Your usual cycle length, Luteal phase length, Day of your cycle todayOpen calculator →
Example answer14 days to next periodToday is day 15 of 28When is my next period?You need: Your usual cycle length, How long your period lasts, Days since your period startedOpen calculator →

Why cycle timing is harder than it looks

The luteal phase — ovulation to period — is the stable part of a cycle at roughly 14 days. The follicular phase is what varies. So ovulation is estimated backwards from the next period, not forwards from the last, and a 35-day cycle ovulates around day 21 rather than day 17.

Even done correctly, calendar prediction is limited. More than half of women vary by over a week across a year, and ovulation shifts with stress, illness and travel. ASRM suggests intercourse every one to two days across the cycle rather than aiming at a predicted date.